The present invention relates to superconductor joints and more particularly to easily testable superconductor joints.
Superconductivity is the property of certain materials at cryogenic temperatures approaching absolute zero to carry currents without power dissipation. To establish the superconducting or persistent mode, an electromagnet wound with superconducting wire is cooled to superconducting temperature and energized with an external direct current power supply. Liquid helium is usually used to cool superconducting devices to about 4.2.degree. K. When the desired current and magnetic field are established, a switch which joins the coil wire into a continuous loop is closed and the power supply is disconnected. If there are no resistive (non-superconducting) elements in the loop, the current and the magnetic field will remain constant indefinitely.
The switch consists simply of a section of wire heated to make it normal (resistive). Therefore, at least one wire-to-wire joint is needed for a magnet to complete the loop. For magnets with more than one coil, it is difficult or impossible to wind all coils with one continuous piece of wire, and several joints are required. For the persistent mode, such joints must not go normal when subjected to magnetic fields during operation of the magnet.
The method currently in use to determine the integrity of the superconducting electrical connections involves making test sample joints just prior to and immediately after making the magnet coil joints. The test joints are then evaluated by testing the joints in a superconducting environment (4.2.degree. K.) for the values of persistent and quench current. If the samples made just prior to and immediately after the magnet connection prove to be satisfactory, it is then assumed that the magnet connection is also acceptable. The initial testing of the electrical connection themselves is not done until the entire magnet system is completely assembled and hermetically sealed in a cryostat. If a defective connection should be present, an intensive dismantling of the cryostat and considerable disassembly of the magnet system is required to perform the joint repairs. A 1.5 Tesla superconducting magnet can have over 35 superconducting joints.
It is an object of the present invention to provide an electrical coil connection for a superconducting magnet which can be checked for integrity and persistent behavior immediately after the connection is made and before further assembly of the magnet system.
It is a further object of the present invention to provide an electrical coil connection for a superconducting magnet which can be immediately checked for integrity and persistent behavior without requiring that the complete magnet be placed in a 4.2 K. environment.